Allow only one submission

airoid

How can I allow only one submission on my PHP form? I don't want the visitor to be able to come back a couple days later and fill out the form again. Do I use cookies? If so, how? Anyone know????

n00854180t

If you used cookies they could just clear them and submit again.

SpanKie

Depending on how your site is setup. If your using a user base system (such as the user has to login before they can fill out the form) you can put a test on the form page to query the database and check it the user has previously submitted data. Another way, but not completely full proof is you can use the visitors IP to verify against. Store it in a table or flat file .

Sxooter

Here's an easy trick, use the random string like this:

$string = md5(time());

and put it in a hidden field in your form. then, insert that into a field that has a unique constraint. That way, when the use submits the same form again, they'll generate a unique key violation in the database and the entry wont get submitted.

airoid

Great suggestions. SpanKie, do you have any code for the suggestions that you gave me? I can use the mysql database but I'm not sure what code I would implement. Sxooter, I'm not sure that I understand what you are talking about. Could you explain further? I'm not a novice but I'm not the most experienced guy ever.

n00854180t

Sxooter's example would work like this:

First you make a hidden field on your form which will host the value of $string = md5(time());
So you would have for instance $hiddenname = $string;

Then you make a field in your database that is a varchar(60) field that is a unique id. When the user submits the form to the database insert the value of the hidden field into your varchar field. Then if they try to submit the form again it will generate a unique key violation like Sxooter said. Although I think you should use something else as the argument for the md5() function (something that can't be changed).

Sxooter

A couple of variations on that, one is the use the nextval('seq') from a pgsql database and put it into the form and then insert it into a unique key, the other, and one I like a lot, is to md5 the whole posting, and then insert that as the unique key. In that instance, if the user accidentally hit back/submit, it wouldn't take the message, but if they change a character, it would.

airoid

Okay these are good....now I want to be able to send the user straight to the "thank you" page if they have already submitted the form and happen to fill it out and submit it again. Any suggestions on how to do this?

Sxooter

<?php
header("location: thanks.html");
?>

Note there can be NO WHITESPACE before the <?php opening tags.